Flow energy harvesting with piezoelectric flags

In this article, energy harvesting with a fluttering cantilevered plate covered by piezoelectric patches in an axial flow is adressed. A theoretical model is presented which is then discretized and numerically integrated to perform a parametric study of the energy harvesting efficiency of the system. When one, two or three piezoelectric patches cover the plate, the optimal distributions of the patches that maximize the efficiency are obtained. Experimental results are presented, which are in good agreement with the model. When a significantly high number of patches of small size are considered, a continuous model is used to study the influence of a resonant harvesting circuit. A lock-in phenomenon is evidenced, which is able to significantly increase the efficiency. Published in the proceedings of 33rd International Conference on Ocean, Offshore and Arctic Engineering OMAE2014, June 8-13, 2014, San Fransisco, USA Paper no OMAE2014-23867 I INTRODUCTION Recent efforts in the developement of new energy harvesting methods have been focused on the study of fluid-solid coupled systems that allow the conversion of the kinetic energy of flows into electrical energy [1, 2]. Apart from the classical technologies such as wind and water turbines, other techniques involving the deformation of elastic structures under the action of fluid forces have attracted the attention of several research groups. The present study is focused on the energy harvesting from the fluttering of a piezoelectric flag in an axial flow [3, 4]. A flexible plate in an axial flow can become unstable and develop self sustained flapping if the flow velocity exceeds a critical value. If the flapping plate is made of a piezoeletric material, the plate’s deformation can be transformed into electrical energy. Previous works [5, 6] have studied the fully coupled dynamics of a flexible plate covered by an infinite number of piezoelectric patches connected to simple resistive circuits. The case of a unique piezoelectric patch covering the entire length of the plate has also been considered [7]. The first question addressed in the present paper is the influence of the number and dimensions of the piezoelectric patches on the harvesting efficiency. Existing studies on the damping of vibrations with piezoelectric patches connected to passive circuits considered the influence of a resonant circuit [8]. This motivates the second question in the present paper: what is the influence of a resonant circuit on the non-linear dynamics of the system, and the resulting harvesting efficiency? The paper is organized as follows. In section II, we present a non linear dynamic model of a plate in an axial flow coupled to electrical circuits trough piezoelectric patches. Continuous and discrete configurations are presented. The numerical methods are also briefly described. Next, a parametric study of the influence on the number and geometries of the piezoelectric patches is presented. In this section, some experimental results are also compared to numerical results. Finally, a study of the influence of a resonant circuit on the energy harvesting efficiency is presented.